System and method for blind channel estimation and coherent differential equalization in an orthogonal frequency division multiplexing (ofdm) receiver

ABSTRACT

In one aspect, an apparatus includes: a fast Fourier transform (FFT) engine to receive and convert a plurality of orthogonal frequency division multiplexing (OFDM) samples into a plurality of frequency carriers; a detector coupled to the FFT engine to determine a channel estimate for a first frequency carrier using a first channel estimate for the first frequency carrier and a plurality of other channel estimates, each of the plurality of other channel estimates for one of a plurality of neighboring frequency carriers within an evaluation window, and determine a log likelihood ratio (LLR) for the first frequency carrier using the channel estimate for the first frequency carrier; and a decoder coupled to the detector to decode a first OFDM symbol comprising the first frequency carrier using the LLR for the first frequency carrier.

CROSS REFERENCE

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND

Radio receivers are omnipresent in modern technology. In addition tostandalone radios for receipt of broadcast radio signals, all manners oftech and non-tech devices include some type of radio receiver (and oftenpaired with a transmitter). Such modem circuitry is present in anydevice having wireless capabilities. While some broadcast radio signalsare transmitted with analog modulation (e.g., conventional AM and FMsignals), other terrestrial and satellite wireless communication systemsuse some type of digital modulation. Some example digital radio systemsinclude National Radio System Committee (NRSC-5C, also known as HD™radio), Digital Audio Broadcasting (DAB), Digital Radio Mondiale (DRM)or other standard.

Channel estimation is an operation performed in a receiver to determinechannel conditions. In some example digital radio communication systems,message information is communicated in orthogonal frequency divisionmultiplexing (OFDM) symbols. Unlike certain other digital radiocommunication systems, in a DAB system there are no pilot symbols orother reference information communicated within a signal stream that canbe used for purposes of determining channel conditions by way of achannel estimate. In DAB differential modulation is used so non-coherentdemodulation without channel estimation is typically performed, but suchdemodulation has lower performance than coherent demodulation.

SUMMARY OF THE INVENTION

In one aspect, an apparatus includes: a front end circuit to receiveincoming radio frequency (RF) signals and process the incoming RFsignals into orthogonal frequency division multiplexing (OFDM) samplesof a plurality of OFDM symbols; a fast Fourier transform (FFT) enginecoupled to the front end circuit, the FFT engine to receive theplurality of OFDM samples and convert the plurality of OFDM samples intoa plurality of frequency carriers; a detector coupled to the FFT engine,the detector to determine a channel estimate for a first frequencycarrier using a first channel estimate for the first frequency carrierand a plurality of other channel estimates, each of the plurality ofother channel estimates for one of a plurality of neighboring frequencycarriers within an evaluation window, and determine a log likelihoodratio (LLR) for the first frequency carrier using the channel estimatefor the first frequency carrier; and a decoder coupled to the detectorto decode a first OFDM symbol comprising the first frequency carrierusing the LLR for the first frequency carrier.

In an example, the detector is to determine the channel estimate for thefirst frequency carrier comprising an average value determined using thefirst channel estimate and the plurality of other channel estimates. Theevaluation window may include a first plurality of frequency carriers ofthe first OFDM symbol and a second plurality of frequency carriers of asecond OFDM symbol adjacent to the first OFDM symbol.

In an example, the detector is to: calculate a plurality of metrics forthe first frequency carrier and the plurality of neighboring frequencycarriers within the evaluation window; and determine the LLR for a pairof frequency carriers comprising the first frequency carrier and asecond frequency carrier based at least in part on the plurality ofmetrics. The detector may determine the LLR for the pair of frequencycarriers comprising the first frequency carrier and the second frequencycarrier comprising: for a first bit of the first OFDM symbol, adifference between a first maximum metric of the plurality of metricsfor a first value for the first bit and a second maximum metric of theplurality of metrics for a second value for the first bit; and for asecond bit of the first OFDM symbol, a difference between a firstmaximum metric of the plurality of metrics for the first value for thesecond bit and a second maximum metric of the plurality of metrics forthe second value for the second bit.

In an example, the detector may include: a channel estimation circuit togenerate a plurality of channel estimates for the first frequencycarrier, the plurality of channel estimates including the first channelestimate; and a channel estimation smoother to determine the channelestimate for the first frequency carrier using the first channelestimate and the plurality of other channel estimates. The detector mayalso include: a metric calculator coupled to the channel estimationsmoother to calculate the plurality of metrics using the first channelestimate; and a buffer to store the plurality of metrics. The detectormay further include a determination circuit coupled to the metriccalculator to determine the LLR for the pair of frequency carriers andthe plurality of neighboring frequency carriers within the evaluationwindow.

In another aspect, a method includes: determining, in a channelestimation circuit of a receiver, a plurality of channel estimateswithin an evaluation window having a plurality of frequency carriersincluding a first frequency carrier, each of the plurality of channelestimates for one of the plurality of frequency carriers; calculating,in a calculation circuit of the receiver, a plurality of metrics foreach of the plurality of frequency carriers using at least some of theplurality of channel estimates; and determining a soft decision for thefirst frequency carrier based at least in part on the plurality ofmetrics.

Determining a first channel estimate for the first frequency carrier mayinclude calculating an average of an initial channel estimate for thefirst frequency carrier and initial channel estimates for a plurality ofother frequency carriers of the plurality of frequency carriers. Themethod may include selecting the initial channel estimate for theplurality of other frequency carriers comprising a channel estimateclosest to the initial channel estimate for the first frequency carrier.

In an example, calculating the plurality of metrics comprises:calculating a LLR metric for each of the plurality of frequency carriersof the evaluation window, the first LLR metric corresponding to alikelihood that a first bit of a modulation point of the frequencycarrier is a first value; calculating a second LLR metric for each ofthe plurality of frequency carriers of the evaluation window, the secondLLR metric corresponding to a likelihood that the first bit of themodulation point is a second value; calculating a third LLR metric foreach of the plurality of frequency carriers of the evaluation window,the third LLR metric corresponding to a likelihood that a second bit ofthe modulation point is the first value; and calculating a fourth LLRmetric for each of the plurality of frequency carriers of the evaluationwindow, the fourth LLR metric corresponding to a likelihood that thesecond bit of the modulation point is the second value.

In an example, the method further comprises determining a first LLRvalue and a second LLR value based at least in part on the first LLRmetric, the second LLR metric, the third LLR metric, and the fourth LLRmetric. The soft decision may include the first LLR value and the secondLLR value. The method may further include performing coherentdemodulation for a differentially encoded quadrature phase shift keyingorthogonal frequency division multiplexing symbol using the softdecision.

In yet another aspect, an apparatus comprises: means for determining aplurality of channel estimates within an evaluation window having aplurality of frequency carriers including a first frequency carrier,each of the plurality of channel estimates for one of the plurality offrequency carriers; means for calculating a plurality of metrics foreach of the plurality of frequency carriers using at least some of theplurality of channel estimates; and means for determining a softdecision for the first frequency carrier based at least in part on theplurality of metrics. In an example, the means for determining is tocalculate an average of an initial channel estimate for the firstfrequency carrier and initial channel estimates for a plurality of otherfrequency carriers of the plurality of frequency carriers.

The apparatus may further include means for selecting the initialchannel estimate for the plurality of other frequency carrierscomprising a channel estimate closest to the initial channel estimatefor the first frequency carrier. The means for calculating may include:means for calculating a first LLR metric for each of the plurality offrequency carriers of the evaluation window, the first LLR metriccorresponding to a likelihood that a first bit of a modulation point ofthe frequency carrier is a first value; means for calculating a secondLLR metric for each of the plurality of frequency carriers of theevaluation window, the second LLR metric corresponding to a likelihoodthat the first bit of the modulation point is a second value; means forcalculating a third LLR metric for each of the plurality of frequencycarriers of the evaluation window, the third LLR metric corresponding toa likelihood that a second bit of the modulation point is the firstvalue; and means for calculating a fourth LLR metric for each of theplurality of frequency carriers of the evaluation window, the fourth LLRmetric corresponding to a likelihood that the second bit of themodulation point is the second value.

The apparatus may further include means for determining a first LLRvalue and a second LLR value based at least in part on the first LLRmetric, the second LLR metric, the third LLR metric, and the fourth LLRmetric.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a graphical illustration of a plurality of frequency carriersin accordance with an embodiment.

FIG. 1B is a graphical illustration of a received signal via a channelin accordance with an embodiment.

FIG. 2 is a block diagram of a receiver in accordance with anembodiment.

FIG. 3 is a graphical illustration of a plurality of OFDM modulatedfrequency carriers in accordance with an embodiment.

FIG. 4A is a graphical illustration of a channel estimation for afrequency carrier in accordance with an embodiment.

FIG. 4B is a graphical illustration of four possible channel estimatesin accordance with an embodiment.

FIGS. 4C and 4D are graphical illustrations of neighboring channelestimates used in accordance with an embodiment.

FIGS. 5A and 5B are graphical illustrations of possible modulationpoints for a received frequency carrier.

FIG. 6 is a graphical illustration of an evaluation window in accordancewith an embodiment.

FIG. 7 is a block diagram of a coherent differential equalizationcircuit in accordance with an embodiment.

FIG. 8 is a flow diagram of a method in accordance with an embodiment.

FIG. 9 is a block diagram of a representative device in accordance withan embodiment.

DETAILED DESCRIPTION

In various embodiments, a radio receiver is implemented with adifferential detector circuit that is configured to efficiently estimatea channel for an incoming radio frequency (RF) signal and to generatesoft decisions based at least in part on the channel estimates.Embodiments may be used in a variety of receiver implementations fordetermining and using channel estimates to obtain soft decisions forincoming orthogonal frequency division multiplexing (OFDM)communications. While embodiments are not limited in this regard,implementations may be used in connection with a Digital Audio Broadcast(DAB) digital radio communication system according to a givenspecification. Other implementations can be used in connection withother digital communication techniques, including wireless local areanetworks or other receivers using OFDM signaling.

While a differential detector circuit can be implemented in differentmanners, in embodiments herein this circuit may be implemented as partof a receiver signal processing path that receives downconverteddigitized symbols in the frequency domain (after conversion from thetime domain to the frequency domain). With embodiments, a blind channelestimate can be performed based on the knowledge that an incoming symbolprovides information of one of a limited set of known values. Using thischannel estimation allows coherent demodulation to occur, which gives aperformance gain over non-coherent demodulation.

An OFDM signal is processed mostly in the frequency domain. Due to theproperties of OFDM modulation in which message information includes acyclic prefix and message content, each signal can be presented as:

Y _(i) =X _(i) H _(i) +N _(i)[Equation 1]

where:

-   -   Y_i is the complex value of an input signal at frequency i,    -   H_i is the complex value of the channel at frequency i,    -   X_i is the complex value of the transmitted modulation symbol i,        and N_i is the complex gaussian noise sample.

The goal of channel estimation is to estimate H 1 for every data cell ona time-frequency grid. In an DAB symbol stream in which differentiallyencoded quadrature phase shift keying (DEQPSK) OFDM symbols arecommunicated, there are no pilot or other reference signals at knownlocations that can be used for determining channel estimations. As such,channel estimates may be performed according to a blind channelestimation technique where the fact that an incoming symbol can presentone of four possible values (namely one of four 2-bit combinations) canbe leveraged.

Referring now to FIG. 1A, shown is a graphical illustration of aplurality of frequency carriers for multiple OFDM symbols having DEQPSKmodulation. More specifically as shown in FIG. 1A, graphicalillustration 10 includes multiple OFDM symbols (e.g., X OFDM symbols) 15₀-15 _(X). After conversion from the time domain to the frequencydomain, each OFDM symbol 15 is represented by a plurality of OFDMfrequency carriers (e.g., N frequency carriers) such that each OFDMsymbol 15 is represented by a plurality of frequency carriers 15_(0, 0)-15 _(0, n). Note that the four constellation points of eachsucceeding OFDM symbol 15 are phase shifted from its predecessor by 45°.In a DEPSK modulation scheme, information is encoded in the change ofphase of every frequency carrier 15. In a DAB system implementation, acommunication frame may include 76 OFDM symbols, where each OFDM symbolis transformed, e.g., in a fast Fourier transform (FFT) engine, into2048 frequency bins, with 1536 frequency bins carrying data.

Referring now to FIG. 1B, shown is a graphical illustration of areceived signal via a channel. As shown in FIG. 1B, an OFDM symbol 20,after conversion to the frequency domain, includes a plurality offrequency carriers 20 ₀-20 _(n). Given a channel having some level ofimpairment, frequency carriers 20 have different magnitudes and phases.

Referring now to FIG. 2 , shown is a block diagram of a receiver inaccordance with an embodiment. As shown in FIG. 2 , receiver 200 mayinclude a signal processing path having various components. Embodimentscan be incorporated in different types of receiver systems. In someembodiments, receiver 200 may be a single-die integrated circuit such asa CMOS die having mixed signal circuitry including both analog anddigital circuitry.

With reference to receiver 200, an incoming RF signal that includesdigital radio signals according to a given digital broadcastspecification may be received over the air via an antenna 205. As usedherein, the terms “digital radio” or “digital radio broadcast signal”are used interchangeably and are intended to correspond to broadcastradio communication that occurs digitally. Such communications may be inaccordance with various standards such as a DAB or other standard.

As shown in FIG. 2 , an incoming RF signal received via antenna 205 isprovided to a low noise amplifier (LNA) 210, which amplifies the RFsignal. In turn, LNA 210 is coupled to a filter 215, which may performfiltering of the received RF signal. Understand while shown with two RFfront end blocks, a receiver may include additional RF front endcircuitry in other examples. In turn, the filtered RF signal is providedto a mixer 220, which in an embodiment may be implemented as a complexmixer. In embodiments herein mixer 220 may downconvert the RF signal toa lower frequency signal using a mixing signal received from a clockgenerator 225. In an embodiment, clock generator 225 may be implementedas a local oscillator, phase lock loop or other such clock generationcircuit. In a particular embodiment, this lower frequency signal may be,e.g., a low-intermediate frequency (IF) or zero-IF signal. Thisdownconverted signal is an in-phase/quadrature phase (IQ) signal.

The resulting downconverted signal is provided to an analog-to-digitalconverter (ADC) 230, where the signal can be digitized into a digitalsignal. Note that in some embodiments, either before or afterdigitization, channelization may be performed to generate a channelizedsignal. In an OFDM system, a plurality of samples forms an OFDM symbolof an incoming data stream.

In turn, samples are provided to a buffer 240, which may be implementedas a first in first out (FIFO). The incoming samples are stored inbuffer 240, and are then output to a main digital signal processing pathincluding a fast Fourier transform (FFT) engine 260, which generatesfrequency domain OFDM symbols from incoming time domain OFDM symbols. Inone embodiment, each incoming time domain OFDM symbol can be processedby FFT engine 260 into a plurality of frequency carriers. Note that thenumber of frequency carriers corresponding to a given OFDM symbol mayvary depending upon a particular radio standard, bandwidth of the signaland time duration of the OFDM symbol (without cyclic prefix).

As further shown in FIG. 2 , frequency carriers generated in FFT engine260 are provided to a differential detector 270. In embodiments herein,differential detector 270 may be a dedicated hardware circuit or amicrocontroller or other control logic to execute instructions stored ina non-transitory storage medium such as firmware and/or softwareinstructions. Differential detector 270 may be implemented as a coherentdifferential equalizer to perform channel estimations and use thechannel estimate information to generate soft decisions, e.g., in theform of log likelihood ratio (LLR) values, as described herein. Ofcourse, differential detector 270 could be implemented in different waysin other embodiments.

In embodiments herein, differential detector 275 may generate LLR valuesfor each pair of frequency carriers of the OFDM symbol. In turn, theseLLR values may be provided to a channel decoder 280. In an embodiment,channel decoder 280 may be implemented as a Viterbi decoder to decodeencoded message information based at least in part on the LLR values.Channel decoder also may be used to perform error correction andinformation bit extraction. The resulting demodulated signal may beprovided to an audio processor 290 for audio processing. The encodedaudio signal is then provided to an audio source decoder (not shown forease of illustration in FIG. 2 ) to generate source audio. Althoughshown as individual components, understand that portions of the receiverafter ADC 230 to the end of the signal processing path of FIG. 2 can beimplemented in a digital signal processor (DSP).

Referring now to FIG. 3 , shown is a graphical illustration of aplurality of OFDM modulated frequency carriers in accordance with anembodiment. As shown in FIG. 3 , graphical illustration 300 shows aplurality of frequency carriers 312 (only a representative one of whichis enumerated in FIG. 3 ). As illustrated, for each time instant (on theX-axis) representing an OFDM symbol, a plurality of frequency carriers312 are provided (illustrated on the y-axis)

As further shown in FIG. 3 , an evaluation window 310 is present. Aswill be described herein, samples within evaluation window 310 may beprocessed in determining LLR values for a given one or more of frequencycarriers 312 within evaluation window 310. As such, evaluation window310 may act as a moving window to enable efficient and accuratedetermination of LLR values for given frequency carriers. This is so, astypically the channel changes slowly in both frequency and time. Assuch, it may be assumed that within an evaluation window such asevaluation window 310, the channel is approximately constant.

Referring now to FIG. 4A, shown is a graphical illustration of a channelestimation for a frequency carrier in accordance with an embodiment. Asshown in FIG. 4A, graphical illustration 400 presents four possiblemodulation points 405 ₀-405 ₃ for a frequency carrier. As further shown,a received signal Yi 410 also is illustrated. Note that there may bemultiple, namely four, possible channel estimates per frequency carrier.with the modulation points {1,j,−1,−j}, one of the 4 channel estimates(Yi; 1j*Yi; −Yi; −1j*Yi) will fall on received signal 410, becauseh_est=Yi/mod_point. Accordingly, referring now to FIG. 4B, shown is agraphical illustration of four possible channel estimates h₀-h₃ for agiven frequency carrier.

A channel estimate can be determined solely by using information of asingle carrier; however there may be excessive noise which may impactaccuracy. In embodiments, information of neighboring carriers may beconsidered in determining channel estimates. As such, some averaging maybe performed, leveraging information from one or more neighbor carriersto a given carrier at issue.

To average between channel estimates in accordance with an embodiment,any one of the four channel estimates for a carrier under analysis maybe selected. Thus with reference back to FIG. 4B, assume that channelestimate h₀ is selected. Next, channel estimates from one or moreneighboring carriers can be selected as well. Referring to FIGS. 4C and4D, channel estimates for neighboring carriers are shown, with relationto the selected channel estimate h₀ for a carrier under analysis. Thusas shown in FIG. 4C, from four channel estimates h₀′-h₃′ for a firstneighboring carrier, channel estimate h₀′ is selected since it isclosest to h₀. And in turn with regard to FIG. 4D, from four channelestimates h₀″-h₃″ for a second neighboring carrier, channel estimate h₀″is selected since it is closest to h₀.

Thus with these selected channel estimates of three neighboringcarriers, a channel estimation may be performed, e.g., according to asimple average, as shown in Equation 2.

h _(est)=(h ₀ +h ₀ ′+h ₀″)/3  [Equation 2]

Note that while Equation 2 may be used to perform a simple average fordetermining a channel estimate, in other cases a weighted average may beused; however, a performance impact of such weighted average calculationmay be negligible such that the simpler average calculation instead maybe used, in an embodiment. Note that these 3 channel estimates are forillustration purpose; in embodiments, N×M channel estimates can be usedfor averaging using a moving window, where N is how many carriers'channel estimates are used from the current OFDM symbol (frequency axis)and M is how many carriers' channel estimates are used from other OFDMsymbols (time axis), where N and M are configurable.

Note that any one of the channel estimates for a carrier under analysismay be selected. This is so, as each of the other channel estimates havea known relation to h₀, as shown in Equations 3-5.

hest(1)=hest(0)*exp(1jpi/2)  [Equation 3]

hest(2)=−hest(0)  [Equation 4]

hest(3)=hest(0)*exp(−1jpi/2)  [Equation 5]

Note that using any of hest(0), hest(1), hest(2) and hest(3) in the LLRcalculation will give identical results due to the symmetric nature ofthe modulation points. Various LLR calculations may be performed basedat least in part on this channel estimate determined using a selectedchannel estimate of multiple neighboring carriers. To illustrate theseLLR calculations, consider modulation points that are generated as aresult of encoding in a transmitter.

Referring now to FIGS. 5A and 5B, shown are graphical illustrations ofpossible modulation points for a received frequency carrier. As shown inFIGS. 5A and 5B two neighboring carriers, namely a first frequencycarrier at symbol k−1 in FIG. 5A and a succeeding carrier at symbol k inFIG. 5B, each may have four possible modulation points 505 ₀-505 ₃ and515 ₀-515 ₃, respectively. In addition, as shown each illustration alsoincludes a received signal, 510 and 520, respectively. With thisarrangement, Equations 6 and 7 illustrate representative LLRcalculations for each respective bit (of a 2-bit value).

$\begin{matrix}{{{LLR}(0)} = {{\max\limits_{a \in {({{{bit}(0)} = 1})}}{Re}\left\{ {C_{k - 1}*h*\left( {x_{k}a*{+ x_{k - 1}}} \right)} \right\}} - {\max\limits_{a \in {({{{bit}(0)} = 0})}}{Re}\left\{ {C_{k - 1}*\left( {h*\left( {x_{k}a*{+ x_{{k - 1})}}} \right.} \right.} \right\}}}} & \left\lbrack {{Equation}6} \right\rbrack \\\left. {{{LLR}(1)} = {{\max\limits_{a \in {({{{bit}(1)} = 1})}}{Re}\left\{ {C_{k - 1}*h*\left( {x_{k}a*{+ x_{k - 1}}} \right)} \right\}} - {\max\limits_{a \in {({{{bit}(1)} = 0})}}{Re}\left\{ {C_{k - 1}*\left( {h*\left( {x_{k}a*{+ x_{{k - 1})}}} \right.} \right.} \right.}}} \right\} & \left\lbrack {{Equation}7} \right\rbrack\end{matrix}$

According to these Equations, the LLR represents a measure of thelikelihood that a given bit of a symbol is a logic 0 or logic 1 value.In Equations 6 and 7, the following values are used:

-   -   C_(k-1)—modulation point after encoder (4 options)    -   h—channel estimation    -   x_(k)—received signal    -   a—information phase change, a={exp(jpi/4), exp(3jpi/4),        exp(5jpi/4), exp(7jpi/4)}

In the above Equations, half of the ‘a’ values correspond to bit=0 andthe other half correspond to bit=1. These halves are different forLLR(0) and LLR(1). Also note that in DAB, differential encoding isapplied across the time dimension, but embodiments are also applicablein the case when differential encoding is applied across the frequencydimension. With Equations 6 and 7 above, to check all possiblemodulation point values for corresponding frequency carriers of twosymbols, 8 calculations may be performed for each of the possible phasechanges. However, in certain hardware implementations, variousoptimizations can be performed to reduce these number of calculations asinformation phase change may only take on two of the four possiblevalues.

While the above Equations 6 and 7 may be used to identify LLR values fortwo bits of a modulation point using information from a singleneighboring sample (i.e., for a common frequency carrier of two adjacentsymbols), embodiments may more accurately determine LLR values usinginformation obtained from multiple frequency carriers of a plurality ofsymbols within an evaluation window.

To this end, embodiments may leverage information from one or moreneighboring symbols to a symbol under analysis and further may leverageinformation of neighboring frequency carriers of both the symbol ofinterest and one or more neighboring symbols.

Referring now to FIG. 6 , shown is a graphical illustration of anevaluation window in accordance with an embodiment. As shown in FIG. 6 ,a graphical illustration 600 includes a plurality of frequency carriers(representative carriers of two adjacent OFDM symbols k−1 and k areenumerated). As further shown, an evaluation window 610 includes aplurality of frequency carriers of these two symbols. In addition,channel estimates h₁-h₆, each associated with a given one of thefrequency carriers, are illustrated. In embodiments herein, channelestimation information from these 6 frequency carriers may be used indetermining LLR values for a given phase change between 2 carriers (herea carrier associated with channel estimate h₁). Understand while in FIG.6 , evaluation window 610 is illustrated that includes carriers of twoadjacent symbols, and is further formed of three adjacent frequencycarriers in each of these symbols, embodiments are not limited in thisregard and larger or smaller evaluation windows may be used in otherembodiments. In some embodiments, a control circuit of a receiver maydynamically configure the size of the evaluation window based onoperating conditions, modulation scheme or so forth.

Techniques to efficiently determine LLR values in accordance withembodiments may be performed in various locations. For example, someimplementations may determine these values in general-purpose processingcircuitry such as a DSP or other programmable controller,microcontroller or so forth that executes instructions stored in anon-transitory storage medium such as firmware and/or softwareinstructions. Instead in other embodiments, dedicated hardware circuitrymay be provided to determine LLR values.

Referring now to FIG. 7 , shown is a block diagram of a coherentdifferential equalization circuit in accordance with an embodiment. Inan embodiment, coherent differential equalization circuit 700 may beimplemented as a differential detector such as differential detector 270of FIG. 2 . As shown in FIG. 7 , coherent differential equalizationcircuit 700 itself may include multiple hardware blocks. Incomingfrequency carriers (X) may be received in a channel estimation circuit710. In embodiments, channel estimation circuit 710 may determine one ormore channel estimates for each incoming carrier. In a particularembodiment, there may be N×M channel estimates determined, with N and Mconfigurable as discussed above. In turn, these N×M channel estimatesare provided to a channel estimation smoother 720. In variousembodiments, channel estimation smoother 720 may include bufferingcircuitry that may be configured to determine a channel estimate for agiven frequency carrier that is an average of channel estimations formultiple frequency carriers including neighboring carriers to a givenfrequency carrier of interest. For example, channel estimation smoother720 may be configured to generate a channel estimate in accordance withEquation 2 above.

Still with reference to FIG. 7 , in turn this channel estimate (h_(m))is provided to a LLR metric calculator 730. In embodiments herein, LLRmetric calculator 730 may generate LLR metrics with respect to a pair offrequency carriers of interest (differential) using information fromthat frequency carrier and additional frequency carriers in anevaluation window with the carrier of interest. To this end, LLR metriccalculator 730 may determine multiple metrics for a given pair offrequency carriers of interest (differential) using Equations 8-11. Notethat the calculated LLR metrics may be stored in a buffer 735 includedin LLR metric calculator 730 or coupled thereto.

In an embodiment these LLR metrics are as follows:

$\begin{matrix}{{{LLR}\left( {{b0},m,1} \right)} = {\max\limits_{a \in {({{{bit}(0)} = 1})}}{Re}\left\{ {C_{k - 1}*h*\left( {x_{k}a*{+ x_{k - 1}}} \right)} \right\}}} & \left\lbrack {{Equation}8} \right\rbrack \\{{{LLR}\left( {{b0},m,0} \right)} = {\max\limits_{a \in {({{{bit}(0)} = 0})}}{Re}\left\{ {C_{k - 1}*h*\left( {x_{k}a*{+ x_{k - 1}}} \right)} \right\}}} & \left\lbrack {{Equation}9} \right\rbrack \\{{{LLR}\left( {{b1},m,1} \right)} = {\max\limits_{a \in {({{{bit}(1)} = 1})}}{Re}\left\{ {C_{k - 1}*h*\left( {x_{k}a*{+ x_{k - 1}}} \right)} \right\}}} & \left\lbrack {{Equation}10} \right\rbrack \\{{{LLR}\left( {{b1},m,1} \right)} = {\max\limits_{a \in {({{{bit}(1)} = 0})}}{Re}\left\{ {C_{k - 1}*h*\left( {x_{k}a*{+ x_{k - 1}}} \right)} \right\}}} & \left\lbrack {{Equation}11} \right\rbrack\end{matrix}$

These metrics rely on the same variables described above as to Equations6 and 7, and may be determined to obtain a likelihood that a given bitof each of m frequency carriers is either a logic 0 or logic 1.

Referring still to FIG. 7 , these LLR metrics may be provided in turn toan LLR determination circuit 740. In embodiments herein, LLRdetermination circuit 740 may determine an LLR value for each ofmultiple bits of a pair of frequency carriers, e.g., using Equations12-13 below. As such, LLR determination circuit 740 outputs these LLRvalues. In an embodiment, the LLR values correspond to a probabilitythat each of the 2 bits (b0-b1) of the carrier are a logic 0 or alogic 1. Note that these LLR values are thus soft decisions for the bitsof the pair of frequency carriers and may be provided to additionalcircuitry of the receiver, such as a channel decoder. Understand whileshown at this high level in the embodiment of FIG. 7 , many variationsand alternatives are possible.

$\begin{matrix}{{{LLR}\left( {b0} \right)} = {{\max\limits_{m = {1:6}}\left\{ {{LLR}\left( {{b0},m,1} \right)} \right\}} - {\max\limits_{m = {1:6}}\left\{ {{LLR}\left( {{b0},m,0} \right)} \right\}}}} & \left\lbrack {{Equation}12} \right\rbrack \\{{{LLR}\left( {b1} \right)} = {{\max\limits_{m = {1:6}}\left\{ {{LLR}\left( {{b1},m,1} \right)} \right\}} - {\max\limits_{m = {1:6}}\left\{ {{LLR}\left( {{b1},m,0} \right)} \right\}}}} & \left\lbrack {{Equation}13} \right\rbrack\end{matrix}$

Referring now to FIG. 8 , shown is a flow diagram of a method inaccordance with an embodiment. More specifically, method 800 is a methodfor determining channel estimates according to a blind channel estimatetechnique and using the resulting channel estimates to calculate LLRvalues. In an embodiment, method 800 may be performed by a hardwarecircuit of a receiver, such as a channel estimation circuit that in turnmay be implemented within a differential detector. Understand that thechannel estimation circuit itself may include or be associated with LLRcalculation circuitry, such as shown in coherent differentialequalization 700 of FIG. 7 .

As shown, method 800 begins by calculating a channel estimation percarrier (block 810). In an embodiment, a selected one of multiplepossible channel estimates for a given frequency carrier may bedetermined. Next at block 820 channel estimates per carrier may bedetermined according to an averaging process. In an embodiment thischannel estimation may be calculated using channel estimates of multiplecarriers within an evaluation window as discussed above.

Still with reference to FIG. 8 , next at block 830 channel estimates maybe collected for an evaluation window. Note that the collected channelestimates can be temporarily stored, e.g., in a buffer. Then at block840 LLR metrics may be calculated for the evaluation window. In anembodiment, such LLR metrics may be calculated according to Equations8-11. Next at block 850 an LLR for bits of a given pair of carriers canbe determined. More specifically as described herein the calculated LLRmetrics for the evaluation window may be used in determining the LLRs,which may occur according to Equations 12-13 above.

Still referring to FIG. 8 , next it is determined whether there areadditional OFDM carriers for a given symbol under analysis (diamond860). If so, control passes to block 810, discussed above. Otherwise theLLRs for the symbol may be buffered and provided as soft decisions to adecoder when a full decoder block is received (block 870), so thatchannel decoding may be performed. Note that a full decoder block mayformed of a given number of OFDM symbols. Understand while shown at thishigh level in the embodiment of FIG. 8 , many variations andalternatives are possible.

For example, as discussed above in determination of LLR metrics, it ispossible to perform certain optimizations to reduce compute complexity.As one example, when considering possible modulation points in, e.g.,any of Equations 8-11, when a multiplication has a factor of e^(jπ/4k)or e^(jπk) the multiplication can be simplified to:

(a+jb)e ^(jπ/4k) (a+jb)e ^(jπk)

(a+b+j(b−a))/sqrt(2) a+jb

(a−b+j(a+b))/sqrt(2) −a−jb

(−a−b+j(a−b))/sqrt(2) b+ja

(b−a−j(a−b))/sqrt(2) −b+ja

Determining each of the four different C_(k-1) can be performed asfollows:

max{Re{C _(k-1*) h _(m*)(x _(k) a*+x _(k-1))}}=max{Re{C_(k-1)(0)*X},Re{C _(k-1)(1)*X},Re{C _(k-1)(2)*X},Re{C _(k-1)(3)*X}}

As another optimization, since these modulation points are 90 degreesfrom each other, the determination may be implemented as below.

MAX(ABS(real(X),ABS(imag(X));

MAX(real(X)−imag(X),real(X)+imag(X))/sqrt(2);

Embodiments may be implemented in many different types of end nodedevices. Referring now to FIG. 9 , shown is a block diagram of arepresentative device 900 which may be a given wireless device. In theembodiment shown in FIG. 9 , device 900 may be a standalone radio, or aradio incorporated into another device such as a sensor, actuator,controller or other device that can be used in a variety of use cases ina wireless control network, including sensing, metering, monitoring,embedded applications, communications applications and so forth.

In the embodiment shown, device 900 includes a memory system 910 whichin an embodiment may include a non-volatile memory such as a flashmemory and volatile storage, such as RAM. In an embodiment, thisnon-volatile memory may be implemented as a non-transitory storagemedium that can store instructions and data, including code forperforming methods including the method of FIG. 8 . Memory system 910couples via a bus 950 to a digital core 920, which may include one ormore cores and/or microcontrollers that act as a main processing unit ofthe device. As further shown, digital core 920 may couple to clockgenerators 930 which may provide one or more phase locked loops or otherclock generation circuitry to generate various clocks for use bycircuitry of the device. As further illustrated, device 900 furtherincludes power circuitry 970, which may include one or more voltageregulators.

Additional circuitry may optionally be present depending on particularimplementation to provide various functionality and interaction withexternal devices. Such circuitry may include interface circuitry 960which may provide interface with various off-chip devices, sensorcircuitry 940 which may include various on-chip sensors includingdigital and analog sensors to sense desired signals, such as speechinputs, image inputs, environmental inputs or so forth.

In addition as shown in FIG. 9 , transceiver circuitry 980 may beprovided to enable transmission and receipt of wireless signals, e.g.,according to one or more digital radio communication standards such asDAB, DRM or HD™ radio, local area wireless communication schemes, suchas a given IEEE 802.11 scheme, wide area wireless communication schemesuch as LTE or 9G, among others. And as shown transceiver circuitry 980includes a coherent differential equalizer circuit 985, which mayperform channel estimations and use the channel estimate information togenerate soft decisions, as described herein. Understand while shownwith this high level view, many variations and alternatives arepossible.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

1. (canceled)
 2. A wireless receiver comprising: a front end circuit toreceive and process radio frequency signals into frequency domain data;a detector configured, based on the frequency domain data, to determinea channel estimate for a first frequency carrier using a first channelestimate for the first frequency carrier and one or more other channelestimates, each of the one or more other channel estimates for one ofone or more neighboring frequency carriers within an evaluation window,the detector further configured to determine a soft decision for thefirst frequency carrier using the channel estimate for the firstfrequency carrier; and a decoder coupled to the detector and configuredto decode encoded message information in the frequency domain data usingthe soft decision.
 3. The wireless receiver of claim 2 wherein thedetector is further configured to determine the channel estimate for thefirst frequency carrier by calculating an average using the firstchannel estimate and the one or more other channel estimates.
 4. Thewireless receiver of claim 2 wherein the soft decision is a loglikelihood ratio.
 5. The wireless receiver of claim 3 wherein theevaluation window includes a first plurality of frequency carriers of afirst orthogonal frequency division multiplexing symbol and a secondplurality of frequency carriers of a second orthogonal frequencydivision multiplexing symbol adjacent to the first orthogonal frequencydivision multiplexing symbol.
 6. The wireless receiver of claim 2wherein the soft decision includes a log likelihood ratio, and thedetector is further configured to: calculate a plurality of metrics forthe first frequency carrier and the one or more neighboring frequencycarriers within the evaluation window; and determine the log likelihoodratio for a pair of frequency carriers including the first frequencycarrier and a second frequency carrier based at least in part on theplurality of metrics.
 7. The wireless receiver of claim 5 wherein thedetector includes: a channel estimator configured to generate aplurality of channel estimates for the first frequency carrier, theplurality of channel estimates including the first channel estimate; anda channel estimation smoother configured to determine the channelestimate for the first frequency carrier using the first channelestimate and the one or more other channel estimates.
 8. The wirelessreceiver of claim 2 wherein the detector and the decoder are implementedin a programmable controller.
 9. The wireless receiver of claim 2wherein the detector and the decoder are implemented in dedicatedhardware circuitry.
 10. The wireless receiver of claim 2 wherein thedecoder is configured to perform coherent demodulation for adifferentially encoded quadrature phase shift keying orthogonalfrequency division multiplexing symbol.
 11. A method of operating awireless receiver comprising: receiving radio frequency signals with afront end circuit of the wireless receiver, and converting the radiofrequency signals into frequency domain data; determining, withprocessing circuitry of the wireless receiver, based on the frequencydomain data, a channel estimate for a first frequency carrier using afirst channel estimate for the first frequency carrier and one or moreother channel estimates, each of the one or more other channel estimatesfor one of one or more neighboring frequency carriers within anevaluation window; determining, with the processing circuitry, a loglikelihood ratio for the first frequency carrier using the channelestimate for the first frequency carrier; and decoding encoded messageinformation in the frequency domain data using the log likelihood ratio.12. The method of claim 11 wherein determining the channel estimate forthe first frequency carrier includes calculating an average using thefirst channel estimate and the one or more other channel estimates. 13.The method of claim 12 wherein the evaluation window includes a firstplurality of frequency carriers of a first orthogonal frequency divisionmultiplexing symbol and a second plurality of frequency carriers of asecond orthogonal frequency division multiplexing symbol adjacent to thefirst orthogonal frequency division multiplexing symbol.
 14. The methodof claim 11 claim wherein decoding encoded message information in thefrequency domain data using the log likelihood ratio includes performingcoherent demodulation for a differentially encoded quadrature phaseshift keying orthogonal frequency division multiplexing symbol.
 15. Awireless receiver comprising: a front end circuit to receive and processradio frequency signals into frequency domain data; a detectorconfigured, based on the frequency domain data, to determine a pluralityof channel estimates within an evaluation window having a plurality offrequency carriers including a first frequency carrier, each of theplurality of channel estimates for one of the plurality of frequencycarriers, the detector further configured to calculate a plurality ofmetrics for each of the plurality of frequency carriers using at leastsome of the plurality of channel estimates, and to determine a softdecision for the first frequency carrier based at least in part on theplurality of metrics; and a decoder coupled to the detector to decodeencoded message information in the frequency domain data using the softdecision for the first frequency carrier.
 16. The wireless receiver ofclaim 15 wherein the detector is further configured to determine a firstchannel estimate for the first frequency carrier by calculating anaverage of an initial channel estimate for the first frequency carrierand initial channel estimates for a plurality of other frequencycarriers of the plurality of frequency carriers.
 17. The wirelessreceiver of claim 16 wherein the initial channel estimate is a channelestimate of the plurality of channel estimates closest to the initialchannel estimate.
 18. The wireless receiver of claim 15 wherein thedetector further includes a buffer configured to store the plurality ofmetrics.
 19. The wireless receiver of claim 15 wherein the detector andthe decoder are implemented in a programmable controller.
 20. Thewireless receiver of claim 15 wherein the detector and the decoder areimplemented in dedicated hardware circuitry.
 21. The wireless receiverof claim 15 wherein the decoder is configured to perform coherentdemodulation for a differentially encoded quadrature phase shift keyingorthogonal frequency division multiplexing symbol.